Process for producing papermaker&#39;s and industrial fabric seam and seam produced by that method

ABSTRACT

The invention disclosed herein relates to the use of laser energy to weld or melt selected locations in papermachine clothing (“PMC”) and other industrial and engineered fabrics. The invention also relates to an improved seam for a papermaker or other industrial fabric that has properties such as strength, durability, openness, adequate number of support points, and fiber support index (FSI) essentially the same as the fabric body. The invention also relates to a fabric having a durable seam, wherein the seam width as measured in the MD is a fraction of the width of a normal seam or a seam that is formed using a conventional technique of equal strength.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority benefits of U.S. Provisional PatentApplication Ser. No. 60/967,489 filed Sep. 5, 2007, the disclosure ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention disclosed herein relates to the use of laser energy toweld or fuse selected locations in papermachine clothing (“PMC”) andother industrial and engineered fabrics.

INCORPORATION BY REFERENCE

All patents, patent applications, documents and/or references referredto herein are incorporated by reference, and may be employed in thepractice of the invention.

BACKGROUND OF THE INVENTION

The present invention relates to the papermaking arts including fabricsand belts used in the forming, pressing, and drying sections of a papermachine, and to industrial process fabrics and belts, TAD fabrics,engineered fabrics and belts, along with corrugator belts generally.

The fabrics and belts referred to herein may include those also used inthe production of, among other things, wetlaid products such as paperand paper board, and sanitary tissue and towel products made bythrough-air drying processes; corrugator belts used to manufacturecorrugated paper board and engineered fabrics used in the production ofwetlaid and drylaid pulp; in processes related to papermaking such asthose using sludge filters and chemiwashers; and in the production ofnonwovens produced by hydroentangling (wet process), meltblowing,spunbonding, airlaid or needle punching. Such fabrics and belts include,but are not limited to: embossing, conveying, and support fabrics andbelts used in processes for producing nonwovens; filtration fabrics andfiltration cloths; and fabrics and belts used for textile finishingprocesses such as calendering and hide tanning.

Such belts and fabrics are subject to a wide variety of conditions forwhich functional characteristics need to be accounted. For example,during the papermaking process, a cellulosic fibrous web is formed bydepositing a fibrous slurry, that is, an aqueous dispersion of cellulosefibers, onto a moving forming fabric in the forming section of a papermachine. A large amount of water is drained from the slurry through theforming fabric, leaving the cellulosic fibrous web on the surface of theforming fabric.

It should be appreciated that these industrial fabrics such as papermachine clothing (PMC) such as the forming fabrics, press fabrics, anddryer fabrics, all take the form of endless loops on the paper machineand function in the manner of conveyers.

Such fabric structures are typically constructed from synthetic fibersand monofilaments by conventional textile processing methods such asweaving, for example. It is often desirable to selectively tailor thefabric structure to affect or enhance a performance characteristicimportant to, for example, the papermaker, such as fabric life, sheetformation, runnability or paper properties.

For fabrics such as those used for the forming of paper and tissueproducts, or for the production of tissue/towel or through-air drying“TAD” fabrics, such fabrics are often times joined by a seam. In thisinstance, the fabric is usually flat woven from yarns, usuallymonofilaments. Each fabric edge has a “fringe” of machine direction(“MD”) yarns. This fringe is rewoven with cross machine direction (“CD”)yarns in the same basic pattern as the fabric body. This process ofseaming to make endless is known to those skilled in the art. The seamarea therefore contains MD yarn ends. The strength of the seam isdependent upon the MD yarn strength, the number of MD and CD yarns used,and the crimp in the MD yarns themselves that physically “lock”themselves around CD yarns to an extent. However, when the fabric isunder operating tension on, for example, a papermaking or tissue/towelmaking machine, these MD yarn ends can literally slip past one anotherand pull out. The “ends” themselves can protrude above the fabric planecausing small holes in the paper/tissue product or can eventually slipenough so that ultimately, the fabric seam fails and the fabric pullsapart. Typically, the width of the seam area, as measure in MD, formedusing conventional techniques range, for example, anywhere between threeand one half to twenty inches or even more.

To minimize this, the yarns in the seam are usually sprayed or coatedwith an adhesive. Unfortunately, this can alter the fluid handlingproperties of the seam area, and the adhesive can also be abraded andwear off.

While the application of heat to partially weld or fuse yarns to eachother in the seam area has been contemplated, the use of heat generallymay cause unacceptable change to the fluid handling properties of theseam area since all yarns are affected and the seam may, for example,have a resultant air permeability different than the fabric body.

Other shortcomings of the prior attempts are that either because of thenumber of yarns used in the MD, or the size of the yarns used,sufficient seam strength cannot be obtained by conventional seamingmethods, even with the additional use of glues/adhesives.

It is known in the paper machine clothing and/or industrial fabric artsto utilize thermal energy to fuse yarns together to form a seam in forexample, a flat woven fabric of machine direction (MD) and cross machine(CD) yarns.

The need to maintain yarn properties as well as fabric properties in theseam area is paramount. Yarns used in PMC and other industrial fabricsare made from oriented polymers such as polyester, and have a desiredshape and size. It is necessary to maintain essentially the yarn size,shape and characteristics after application of thermal energy. However,heat can affect these materials in a variety of adverse ways. Forexample, heat can cause (a) softening above the glass transition pointof a thermoplastic material which effects dimensional changes, or (b)flow by melting above the melt transition point.

Seam openness should be maintained by not causing major distortion ofthe yarns in the seam area. Also, high yarn tensile strength, especiallyin the MD yarns should be maintained or resultant seam strength will beunacceptable.

While some “melt flow” is required to have at least portions of twoadjacent yarns bond to each other and/or bond to CD yarns that theycrossover, no major distortion of the yarn should occur. So there is aneed to balance the desired yarn, seam and fabric properties compared tothe amount and location of the absorbed thermal energy as exemplified inFIG. 1.

Thermal welding of polymers is achieved by either overlapping of the twoMD yarns, for example, to be welded together by some distance, or end toend welding of two yarns, or either of these in conjunction with fusionto a yarn oriented in another direction in the fabric, for example, atleast one CD yarn. Welding can also occur with just one MD yarn weldedto a CD yarn at a crossover.

There have been attempts to use lasers to weld thermoplastic materialstogether, but “weld quality” and over-fusing of the material wassuspect. Such “over-fusing” would be unacceptable for the yarns used inthe fabric applications envisioned.

Laser technology has advanced, producing laser types that would bettercontrol and focus the thermal energy.

A further development based upon the principles of transmission (somelaser wavelengths are transparent to polymeric materials, such aspolyester for example polyethylene terephthalate (PET) and polyamide(PA)) and absorption is to use a radiation absorbing material within apolymer matrix or applying it to for example, a polymeric yarn surfacein a discrete location where thermal fusion or welding is desired. USPatent Application US2004/0056006A1 assigned to The Welding Institute,exemplifies such technology. However, nothing in this applicationaddresses the needs of using a similar approach on adjacent yarns forexample in the seam of a forming or other industrial fabric.

Another example of using laser energy and an energy absorbing materialis taught in PCT Application WO02/057353A2 assigned to EI Dupont DeNumours and Company. Again however, the teachings are for bondingmaterials shaped by injection molding and do not address therequirements of producing fabrics and improved seams in such fabricswhen using oriented polymeric yarns.

Canadian patent application 2,552,009, assigned to Heimbach GMBH & Co.,KG relates to a forming fabric for use in a sheet forming section of apapermachine, having or comprising a textile planar structure in which,in order to enhance inherent stability, intersecting yarns are engagedinto one another at intersection points and in which yarns additionallyare fused to one another, which is characterized in that the planarstructure comprises intersecting first and second yarns, the first yarnshaving the property that they absorb laser energy and can be brought byabsorbed laser energy, to melting temperatures at least at the surface;and that first and second yarns are fused to one another at least atsome of their intersection points.

The application teaches that one of the two yarns contains a laserenergy absorbing material. Further, when addressing the seam area of awoven fabric, the application teaches that in the seam region, firstyarns (that contain the laser energy absorbing material) should bepresent that extend in the transverse direction and are welded to secondyarns extending in the longitudinal direction. In order to achieveparticularly high seam strength there, the first yarns should be presentin a higher concentration in the seam region than in the remainingregion of the forming fabric, and the first and second fabrics (sic)should be welded to one another at as many intersection points aspossible. The longitudinal yarns inserted in correctly woven fashioninto the respectively opposite end during the stitching process are thenfused to the first yarns. This creates the possibility of shortening theseam region without thereby impairing the strength of the seam. In thisfashion the seam region can be reduced from a usual extension of, forexample, 100 mm in the longitudinal region to, for example, 60 mm, i.e.the seam region can be shortened by 20-60% in the machine direction.

However, an apparent major shortcoming of this approach is that theother properties of the seam such as its permeability, number of sheetsupport points, and Fiber Support Index (FSI) will be different from themain fabric body as the end counts in the CD will be different.

Thus, the fusing or welding of synthetic polymeric yarns by focusedlaser energy, especially those in the seam area of woven fabrics,without causing appreciable loss of yarn properties; major alteration ofsize and/or shape of the yarns; having a seam that has properties likethe body of the fabric; that the seam has, if the seam is the samelength in the MD as normally used, higher durability, and strength equalto or higher than an unfused or unwelded seam; and if the seam isshorter in the MD than normally used, strength sufficient to allow thefabric to run a useful life when installed and used on a paper or otherindustrial machine, is the subject of the present invention.

SUMMARY OF THE INVENTION

Surprisingly, the deficiencies of the art are overcome by the objects ofthe invention which are described below:

One object of the invention is to provide an improved seam for apapermaker or other industrial fabric or belt.

Another object is to provide an improved seam for a papermaker or otherindustrial fabric or belt that has properties such as strength,durability, openness, adequate number of support points, and FSIessentially the same as the fabric body.

Another object of the invention is to provide an improved seam in afabric that has minimal terminal yarn end pullback and seam endtermination wear.

Another object of the invention is to provide a seam for wovenstructures from yarns which allows creation of said woven structure andseam which would not have adequate strength using conventional seamingmethods.

Another object of the invention is to enable fabric designs that havenot been commercialized due to the inability to make seams with adequatestrength using conventional seaming technology.

Another object of the invention is to provide appropriate materials indesired locations which will act as laser energy absorbers.

Another object of the invention is to provide a process for applying theappropriate laser energy absorbing materials in the desired locations.

Another object of the invention is to form a fabric having a durableseam, wherein the seam width as measured in the MD is a fraction of thewidth of a normal seam or a seam that is formed using a conventionaltechnique of equal strength. This fraction can be 0.7 or lower,preferably 0.5 or lower, and most preferably 0.3 or lower. For example,if “X” is the width of a seam in MD according to prior practice, or aconventional seaming method, then the width of the seam formed accordingto the instant invention is, for example, 0.7× or lower, preferably 0.5×or lower, and most preferably 0.3× or lower whilst being of equalstrength.

Another object of the invention is to provide seams which contain yarnswhich are grooved to further improve fusion/bonding for increased seamstrength.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more complete detail withreferences being made to the figures wherein like reference numeralsdenote like elements and parts, which are identified below:

FIG. 1 is a graph exemplifying the effect of the amount of laser energyabsorbed on the strength of a polymeric monofilament yarn, and also onthe bond strength of two polymeric monofilaments fused together;

FIGS. 2 (a)-(d) depict one of the problems associated with conventionalwoven seam formation;

FIG. 3 is a picture of a forming fabric, and its seam area, preparedusing an embodiment of the invention;

FIG. 4 (a)-(e) are SEM of yarns usually in an area of the fabric thathave been laser microwelded;

FIGS. 5 (a) and (b) are photos of yarns comparing the effect ofnonaqueous and aqueous laser dyes;

FIGS. 6( a)-(d) depict a same seam termination pair, and also, showinghow stress is distributed through the seam to adjacent MD yarns as theycrossover or under the bordering CD monofilament yarns;

FIGS. 7( a)-(c) show a seam termination consisting two warp ends andalso, showing how stress is distributed on either side;

FIG. 8 is a stylized depiction of the MD and CD yarns in a seam area,the dots representing where the yarn end terminations are located;

FIG. 9 depicts 100% welding according to one embodiment of theinvention;

FIG. 10 shows a group of CD weld stripes, according to one aspect of theinvention;

FIG. 11 shows a group of spot welds, according to one aspect of theinvention;

FIG. 12 shows a preferred welding pattern where a contiguous path ofunwelded fabric is achieved and all of the warp end terminations arewelded;

FIG. 13( a)-(c) show a monofilament, a welded braided structure, and acrossover point in the welded braided structure, according to oneembodiment of the invention; and

FIG. 14( a)-(b) are cross sectional views of a welded fabric, accordingto one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to improving seams in paper machine andother industrial fabrics by utilizing laser energy. The presentinvention, specifically, relates to belts used in the forming, pressing,and drying sections of a paper machine, and to industrial processfabrics and belts, TAD fabrics, engineered fabrics and corrugator belts.In one aspect of the invention there is a need to make a stronger and/ormore durable seam. In another aspect, there is a need to provide seamswith adequate strength that are shorter in the MD than would commonly beused. Another aspect is to be able to provide woven fabric structuresthat heretofore could not be produced due to the inability to provideadequate seam strength using conventional seaming technology.

The present invention also relates to the fabric produced using such animproved seam.

The present invention also relates to a process for producing such animproved seam and fabric.

While most of the discussion will be for seams for flat woven fabrics,other types of seams, such as for example the commonly known pin seam orinline spiral seam, which also requires reweaving of MD yarns into thefabric body and has the potential therefore to fail due to yarn slippageand pull out, can also be improved by the laser welding techniquedescribed herein. In such seams, the MD yarns which form the seam loopsthemselves can be welded or fused to the CD yarns to prevent them frompulling out under operating tensions in use.

Various different methods are envisioned to produce these seams. Onemethod is to focus the laser in discrete locations such as at seamtermination points in the fabric seam. The presence of an absorbingmaterial at each location may be necessary as most polymeric materialsdo not absorb laser energy. Otherwise, the laser energy may causeover-melting and/or loss of molecular orientation where the laser energyis focused on the yarns in the fabric.

One method to incorporate the absorber is to have it be part of thepolymer resin used during extrusion of the yarn itself. Then the lasercan be focused at each desired discrete location causing local fusionand welding.

Another method to incorporate the absorber is to coat the yarns with theabsorbing material prior to weaving them into the fabric. In this case,the laser energy absorbing material, for example a particular dye, isapplied by dye coating on the yarns before being woven into the fabricor sprayed on in a controlled precise pattern after the fabric is wovenand seamed. In a subsequent operation, the laser is focused at eachdesired location, thus, causing local fusion.

Another method to incorporate the absorbing material is to apply it tothe desired discrete locations in the fabric. A method for applyingresin material in discrete locations is taught in commonly assigned U.S.Publication No. 2004/0126569, wherein the laser energy absorbingmaterial can be deposited onto the fabric in a controlled manner so asto create a predetermined pattern of deposits.

Another method is to spray the absorbing material in CD bands in desiredlocations, for example, the seam area, of a woven, seamed fabric.

The basic principle of the use of a laser energy absorbing material isto provide a means for the energy source to heat the surfaces of theyarns in desired locations without appreciable heating of the yarn core.In this way it is possible to heat the yarn surfaces such that thesurfaces can be fused to another yarn without melting the entire yarncross-section. Two neighboring yarns in a seam area 10 of a woven,seamed fabric, for example a CD yarn 14 and an MD yarn 20, as shown inFIG. 3, that have a laser energy absorbing material on their surfacesand that are in contact with each other will fuse or weld together whenthe yarns are exposed to a properly controlled laser source. If too muchenergy is supplied by the laser, the yarns will either destructivelymelt or vaporize. If too little energy is supplied, the fiber surfaceswill not get hot enough to melt and fuse together. When the properamount of energy is supplied, the yarns will fuse together without theyarns losing substantial strength.

FIG. 4( a) is an SEM photo of a multilayer forming fabric that wascoated in one section with a laser energy absorbing material that wasdispersed in a solvent. After the solvent had dried, the fabric wasexposed to a YAG laser for a 1 millisecond pulse at 225 volts. Thediameter of the focused beam of the laser was around 300 microns. Thissingle pulse produced multiple welds throughout the structure in andaround the area of the laser beam. Microwelds are clearly formed betweenmachine direction and cross machine direction monofilaments. Themonofilaments in this photo are comprised of polyethylene terephtholate(PET).

FIG. 4( b) shows a fabric where the pulse length was increased to 1.1milliseconds. Note the damage 28 resulting from the increased pulselength.

FIG. 4( c) shows a third sample that was made in a similar fashion asthe first sample except that the top and bottom surfaces of the coatedfabrics were wiped with a cloth that had been moistened with acetone.This wiping action removed much of the laser energy absorbing materialfrom the top and bottom surfaces of the fabric sample. The result isinternal welding of the yarns in the structure and little melting at theexternal surfaces of the fabric. A cross-sectional view of such a weldis shown in FIGS. 14( a) and 14(b), where internal welding can be seenwithin the structure and little melting or welding at the externalsurfaces of the fabric.

In one embodiment of the invention, this technique was applied to abraided structure 100 comprised of grooved PET monofilament 50. Thebraided structure 100 was formed on a piece of polyolefin tubingmeasuring 6 mm in diameter. The cross section of the grooved PETmonofilament 50 is shown in FIG. 13( a).

This grooved PET monofilament has a nominal diameter of 9.27 mm. Thegrooves in the monofilament allow laser dye to access the area betweentwo monofilaments that are crossed over one another in the braidedstructure 100. This crossover is very much like the crossover thatoccurs in woven fabrics. In common textile structures made frommonofilaments, the monofilaments are typically round or rectangular incross section without any grooves (smooth surfaced). Groovedmonofilaments are used as a means to capture laser energy absorbingmaterial. Smooth surfaced monofilaments have less area and surfacevolume to capture coatings. In addition, when smooth surfacemonofilaments are used in a crossover textile design, for example awoven fabric, there is little or no free space between two smoothsurfaced monofilaments and it is unlikely that the laser energyabsorbing material, for example a particular dye, will penetrate thearea between the monofilaments. By contrast, any dye applied to thecrossover between two grooved monofilaments, or a grooved monofilamentand a smooth surfaced monofilament, is likely to penetrate the areabetween the monofilaments due to flow of the coating along the groovesoccupying the space between the monofilaments. Thus, using groovedmonofilaments one is able to place laser dye in the space between twocrossing over monofilaments.

As noted above, this technique was applied to a braided structure 100comprised of grooved monofilaments 50 as shown in FIG. 13( b). Afterlaser welding, the crossovers 60 in the structure were found to bewelded securely (shown in FIG. 13( c)). Flexing the structure bycompression and elongation of the braid along its axis did not result inthe failure of any welds. By comparison a similar braided structure wasprepared using smooth surfaced PET monofilament. The welded structurewas also subjected to compression and elongation along its axis. As aresult of this compression and elongation, many bonds broke at thecrossovers. It was observed from these weld failures that groovedmonofilaments can be used to form micro-welds that are more durable thanthe micro-welds formed with smooth surfaced monofilament.

The types of micro-welding described above can also be used to increasethe strength and/or durability of, for example, forming fabric seams.Conventional seams rely on fiber/yarn crimp and friction to hold theseam together. By welding together machine direction and cross machinedirection monofilaments in such seams, it is possible to increase thestrength and/or durability of the seams.

This type of micro-welding can also enable new fabric designs to becommercialized. In the past, fabric weave designs having so-called“straight warps” have been considered. Designs that have straight warpsare problematic as the MD yarns in the seam lack sufficient crimp andfriction that are needed to hold the seam together. Otherwise straightwarp designs are very attractive as they enable fabric designs that haveimproved tensile modulus relative to conventional forming fabric designsthat have crimped machine direction monofilaments with sufficient crimpto form a strong seam. Another example is the “straight line” conceptthat involves straight warps residing in the middle of a multi-layerfabric. The warps have insufficient crimp and friction for making aseam. By utilizing the micro-welds described herein, one can enableseams to be made with straight warp fabric designs. Micro-welds betweenmachine direction and cross machine direction monofilaments enablestresses to be transferred around and across a termination in the seamof the fabric structure. Other designs utilizing very fine yarns ineither the MD or CD, or designs that use yarn counts that are relativelylow (meaning coarse fabrics), may not have adequate seam strength unlessthe seam is enhanced by laser micro-welds.

As stated above, another approach to making micro-welds also utilizes alaser dye or laser pigment. In this case the laser dye or laser pigmentis dispersed in the material comprising the monofilament. Typically, theconcentration of the laser dye or laser pigment is less than 0.4%. Thepresence of the laser dye or laser pigment allows one to make an “energyabsorbing” monofilament at the frequency of the energy source.Preferably, a laser energy source is used as lasers are designed todeliver precise amounts of energy to specific locations. FIG. 4( d)shows a polyester monofilament 14 containing 0.3% of a laser dye(Epolight 2057 from Epolin, Inc.) that has been bonded to a“non-absorbing” polyester monofilament 20. The two monofilaments werelaid in contact with each other at 90 degrees. The crossover of the twomonofilaments was exposed to a YAG laser for a 1 millisecond pulse at223 volts. The diameter of the focused beam of the laser was about 300microns. This single pulse welded the two monofilaments together. The“non-absorbing” monofilament 20 was made without any laser dye orpigment so that the monofilament would be non-absorbing at the frequencyof the energy source.

In another case a CD PET monofilament 14 containing 0.4% of a laserabsorber was woven into a fabric as a wear side monofilament. All of theother monofilaments in the fabric were comprised of “non-absorbing” PETmonofilaments 20. A 300 micron diameter area of the fabric was exposedfor 1 millisecond to a YAG laser operating at 225 volts. The area thatwas exposed was the crossover between the CD monofilament and twomachine direction monofilaments. As shown in FIG. 4( e) the CDmonofilament 14 fused and bonded to the machine direction monofilaments20.

If any of the techniques herein described above are utilized in the seamarea of a woven fabric, problems such as seam terminal end pull backand/or holes in the seam area are virtually eliminated. FIG. 2( a)-(d)shows this detrimental phenomena, wherein the terminating ends of thetwo fabric edges are “overlapped” in the seam area and the criticalpoints 12, where these ends might “pullback” in the MD and the endsthemselves might protrude through the paperside surface, are identified(FIG. 2( a)). Eventually the slippage in the overlapping area increasesas shown by the arrows due to increased localized stresses in the fabric(FIG. 2( b)) and there is a complete slippage and a hole 16 appears inthe overlap region of the seam area of the fabric (FIG. 2( c)).Accordingly, the overlap region of the seam is typically reinforced bymanually gluing 18 (FIG. 2( d)) to increase its strength; however,gluing is a laborious and time consuming process. Due to its lowprecision it is also hard to limit the glue to only the overlappingyarns. In addition, the glue eventually fails either due to flexing ofthe fabric and/or abrasion.

Many choices exist for laser energy absorbing materials. The earliestexample was carbon black. The choice of material, the quantity ofmaterial, and the location of the material, all determine the resultantcharacteristic of the fused bond.

As mentioned above, the melting of the yarn occurs on any surface thathas been coated with a laser energy absorbing material and then exposedto the appropriate laser energy source.

In order to control the area or extent of the melting, it has been foundbeneficial to use certain dyes that are water soluble.

When such a dye is applied to a fabric from an aqueous solution andallowed to dry, the dye migrates to the interstices betweenmonofilaments in contact with each other. This is in contrast to otherlaser dyes which are only soluble in organic solvents. These non-aqueousdyes deposit on the entire surface of the monofilament and cause meltingof the entire surface of the monofilament.

FIG. 5( a) illustrates what happens with a non-aqueous laser dye. Notethat the entire surface of the monofilament 20 has been melted afterexposure to laser energy. This can be observed by the mottled surface ofthe monofilament 20 versus the smooth, shiny surface of an unmeltedmonofilament 30. The dye used in this case was Epolight 2057 appliedfrom an acetone solution.

FIG. 5( b) illustrates what happens with an aqueous laser dye (EpolightE2340). Note that the surface of the monofilament 20 is smooth andshiny, while the interstices between monofilaments contain laser dye andare bonded after exposure to laser energy. This result is a significantand unexpected improvement over non-aqueous laser dyes. With respect toforming fabric seams the reduced melting of the monofilament with anaqueous laser dye produces less distortion in the seam area which inturn reduces any potential sheet marking resulting from laser welding.

However, it is a matter of choice which type of dye to use. For example,filled crossover points between MD and CD yarns are advocated for, forexample, forming and TAD fabrics, as the filled crossovers caused bymaterial flow during fusion, reduce the amount of water that wouldnormally reside there due to capillary forces. Reduced water carryingreduces energy cost in paper production. Filled crossovers are alsoadvocated to reduce the accumulation of dirt in the pinch point betweenthe crossovers formed by the MD and CD yarns.

Clearly, a laser welded seam is superior in strength and dimensionalstability to a conventional production seam. While this technologyenables stronger seams, this technology also enables new features to beproduced with conventional forming fabric patterns. This is accomplishedby the impact of welded seam technology on standard heatsettingpractices. Conventional practices of heatsetting are limited due to atrade-off between dimensional stability and seam strength. If one usesharsh heatsetting conditions that result in a large amount of fabricstretch (crimp removal in the MD mono filaments), the resulting productwill have low seam strength, but high dimensional stability. Typicallyharsh heatsetting conditions are not used as they result in a seamstrength that is too low. With laser welded seam technology, heatsettingconditions that are harsher can be used, as the normally low seamstrength is compensated for by the welded seam strength. This means thatthe resulting structure will have better dimensional stability thanconventional fabrics. This also means that more plane difference willresult between the MD and CD monofilaments. This is an advantage in thewear side as this allows one to increase resistance to fabric wearcharacteristics without resorting to the use of large diametermonofilaments. In turn this keeps the fabric caliper low and forexample, reduces water carrying by the forming fabric.

As mentioned above, various methods have been considered to microweldeither crossover points in woven structures, or contacting pointsbetween adjacent yarns in woven structures via laser welding or fusing.

Welds make it possible to transfer machine direction stress around oracross the terminations in the seam area without the integrity of theseam being dependent only upon yarn friction and crimp in the seam area.Welds have been made in various patterns including complete (100%)welding of the entire seam area, regular arrays of spot welds, andgroups of CD weld stripes. A combination of these welds can also beformed e.g., a combination of spot welds and a group of CD weld stripes.The mechanical properties of, for example, a forming fabric seam areamust allow for skew due to misaligned rolls on a paper machine. In thisrespect the seam must be capable of handling shear forces in the planeof the fabric without causing problems such as buckling or wrinkling ofthe fabric during use in the papermaking process. Seam areas which arewelded in their entirety (100% welded in the seam) are stiff and highlyresistant to in-plane shear deformation.

An ideal welding pattern for, as an example, a forming fabric seamaccomplishes two goals. First, the pattern ensures that each and everyterminal warp monofilament terminal end in the fabric seam is welded toa shute monofilament such that machine direction stress can betransferred via welds and continuous monofilament around matching orcorresponding terminal warp ends in the seam. As an alternative,multiple welds can be produced along the length of a single yarn, suchas a warp or weft with the wefts and warps crossing over, respectively,thereby sharing the same load with a number of wefts or warps at thecrossover points, thus eliminating any distortion in the fabric. Thesewelds produce a seam that is very durable on a paper machine. Second,the pattern ensures that there are contiguous paths of unwelded warpsand shutes extending from one side of the seam to the other side of theseam in the machine direction. These contiguous paths of unwelded fabricenable the in-plane shear properties of the seam to be similar to thein-plane shear properties of the body of the fabric. This featureenables the fabric including the seam to successfully manage amaldistribution of stresses that can arise from misaligned rolls on apaper machine. If the fabric cannot manage a maldistribution instresses, the fabric will buckle or wrinkle on the paper machine.

Preferably the contiguous paths of unwelded warps are symmetric withrespect to the machine direction. This feature ensures that the in-planeshear properties are symmetric with respect to the machine direction.

The following is intended to explain the pattern in greater detail.Stress transfer in welded seams assumes that every terminal end must bewelded at some place along its length (preferably at or near eachtermination) in order for machine direction stress to be transferredaround each termination via welds and continuous monofilament in thefabric. While stress transfer in a conventional woven seam makes use ofmonofilament crimp and friction between warp and shute monofilaments,this type of stress transfer is ignored. FIG. 6( a) shows a singletermination of two warp ends 14, and FIG. 6( b) shows two spot welds oneither side of this termination.

FIG. 6( c) illustrates the shortest paths by which stress is transferredaround or across this termination. Each path is defined by a combinationof continuous monofilament and welds which bond monofilaments together.In FIG. 6( c) note that there are two paths of equal length.

An alternative to the location of the spot welds shown in FIG. 6( b) isshown in FIG. 6( d). In this diagram, the spot welds are further awayfrom the actual termination. The shortest paths for transferring stressaround the termination are illustrated in FIG. 6( d). The logic forstress transfer as illustrated in the above diagrams can be applied toany spot weld pattern. Successful stress transfer around a terminationwill result as long as there is a continuous path from one side of theseam to the other side of the seam with this path consisting ofcontinuous monofilaments and spot welds that connect warp and weftmonofilaments.

Alternatively, a termination can consist of two warp ends 14 that passby each other as illustrated in FIG. 7( a). While this termination canbe welded in a way identical to that shown in FIG. 6( b) or FIG. 6( d),it is possible to also weld the two warp ends 14 together as illustratedin FIG. 7( b). In this case, stress can be transferred in a direct pathfrom one warp monofilament to another warp monofilament 14 as shown inFIG. 7( c).

According to one embodiment of the invention, FIG. 8 shows the pattern24 of terminations for a support shute binder (“SSB”) forming fabric,according to one embodiment of the invention. The vertical direction inthis diagram is the same as the machine direction. Each dot in thediagram represents a single terminal warp end. Note that the pattern isregular and that the terminations are spread out over a large area. Inthe machine direction the seam length measures about 3 inches. The twosides of the seam are designated by the dotted lines at the top andbottom of FIG. 8.

In the seam of FIG. 8 welds can be made by complete (100%) welding 26 ofthe seam area, arrays of spot welds, and groups of CD weld stripes. Eachof these is described below. The first to be shown is 100% welding 26 inFIG. 9. Clearly, this weld pattern does not provide any contiguous pathof unwelded warps and shutes extending from one side of the seam to theother side of the seam in the machine direction. This pattern stiffensthe fabric resulting in increased in-plane shear stiffness and a reducedability of the fabric to resist buckling or wrinkling while running on apaper machine. However, the weld pattern does ensure that each and everyterminal warp monofilament in the seam is welded to a shute monofilamentsuch that machine direction stress can be transferred via welds andcontinuous monofilament around matching or corresponding terminal warpends in the seam. This makes the seam very durable.

The next figure, FIG. 10 shows groups of CD weld stripes 26. While thisweld pattern does not provide any contiguous path of unwelded warps andshutes extending from one side of the seam to the other side of the seamin the machine direction the weld pattern does ensure that each andevery terminal warp monofilament in the seam is welded to a shutemonofilament such that machine direction stress can be transferred viawelds and continuous monofilament around matching or correspondingterminal warp ends in the seam. It is to be noted, however, that theunfused stripes between the welded stripes are capable of skewing ormanaging distortion of the fabric to some extent. Experiments have shownthat a pattern such as this is an excellent balance between desired seamproperties and process complexity and cost.

Accordingly, the basic process steps for a fabric with the laser energyabsorbing materials in several CD bands are:

-   -   1. Seamed, unfinished fabric is prepared;    -   2. Seam is cleaned;    -   3. Fabric is loaded into appropriate equipment and tensioned to        a specified level;    -   4. Seam is sprayed with laser dye according to a specific recipe        for the design in a controlled manner, and excess dye may be        removed;    -   5. Seam is welded according to a specific recipe for the design;    -   6. Fabric is cut to width;    -   7. Edges are finished; and    -   8. Fabric is packaged and shipped.

Although an order of steps involved in a process for forming a fabricwith a laser energy absorbing material in CD bands has been listedabove, the order therein is purely exemplary, and does not limit thescope of the invention.

As mentioned previously, however, spot welding of individual locationscan be utilized. The next figure, FIG. 11 shows a group of spot welds26. This weld pattern does provide for a contiguous path of unweldedwarps and shutes extending from one side of the seam to the other sideof the seam in the machine direction. This pattern stiffens the fabriclocally where the spot welds reside. These locally stiff welds do notgreatly increase the in-plane shear stiffness in the seam area. As aresult, this seam design is best able to resist buckling or wrinklingwhile running on a paper machine. However, this particular spot weldpattern does not ensure that each and every terminal warp monofilamentin the seam is welded to a shute monofilament such that machinedirection stress can be transferred via welds and continuousmonofilament around matching or corresponding terminal warp ends in theseam. This happens because the welds are aligned in the machinedirection with a space between each machine direction column of welds.As a result, portions of the seam depend upon friction to transfermachine direction stress from one side of the seam to the other. Thisreduces the durability of the seam.

FIG. 12 shows a preferred welding pattern 26 where a contiguous path ofunwelded warps is achieved and all of the warp end terminations arewelded. This pattern achieves the desired combination of in-plane shearproperties and seam durability. Each and every fabric design and seampattern would require a stylized and specific spot welding pattern toachieve the desired result.

While spot welding can be achieved by just laser energy itself, apreferred method is to use an absorber for laser energy deposited at therequired precise locations which would minimize yarn distortion and lossof molecular orientation of the polymer making up the yarn.

Therefore, a summary of advantages of the present invention can beenlisted as follows:

-   -   Seam strength and durability    -   Seam robustness—ability to withstand abrasive conditions such as        high pressure showers and abrasive fillers used for example, in        paper production    -   Shorter seams in the MD    -   Allow creation of new fabric structures that can be seamed    -   Fabric runs drier in a wet environment such as papermaking    -   Broadening process windows, such as heatsetting, to enhance        fabric characteristics

Therefore, the result of the use of laser welding is a stronger and/ormore durable seam for the same length seam in the MD. As an alternative,preferably, the seam width as measured in the MD is a fraction of thewidth of a normal seam or a seam that is formed using a conventionaltechnique of equal strength. This fraction can be 0.7 or lower,preferably 0.5 or lower, and most preferably 0.3 or lower. For example,if “X” is the width of a seam in MD according to prior practice, of aconventional seaming method, then the width of the seam formed accordingto the instant invention is, for example, 0.7× or lower, preferably 0.5×or lower, and most preferably 0.3× or lower whilst being of equalstrength to the “X” length seam. Although seams for flat woven fabricshave been discussed, the present laser welding technique can be appliedto other types of seams, such as for example a pin seam or inline seam,wherein the MD yarns which form the seam loops themselves and are wovenback into the fabric body can be welded or fused to the CD yarns toprevent them from pulling out under operating tensions in use, thusimproving the seam strength and uniformity in stress or loaddistribution.

EXAMPLES Example I

A double layer fabric was woven and seamed with yarns containing a laserenergy absorbing material. The fabric seam was exposed to the laserenergy source in one area, and left unfused in another area. Sampleswere then removed of the corresponding seam areas, and breaking strengthwas measured. A 53% increase in breaking strength was reported.

Example II

Triple layer SSB fabrics of various designs were woven, and the seamshad laser energy absorbing material present in desired locations. Afterexposure to a laser in one area of the seam, samples were removed ofunfused and fused seam areas. Seam strength increases of up to 129% werereported.

Example III

In another experiment, a triple layer SSB fabric with a shorter (in theMD) seam that contained laser energy absorbing materials in the yarnswas exposed to laser energy in a portion of the seam. Samples of thefused and unfused areas of the seam were tested, and a 47% increase inbreaking strength was reported.

Example IV

An SSB fabric was woven and seamed that had laser energy absorbingmaterials present in desired locations in the seam area. The seam wasexposed to the appropriate laser energy source. The fabric was then runon a pilot machine on the conveying position of a gap forming machinemaking 45 gsm newsprint at 800 mpm. Trial conditions such as fabrictension, counter blade loading, and vacuum levels were varied. No sheetdrainage mark from the seam was detected under the entire range ofconditions employed.

Thus the present invention, its objects, and advantages, are realizedand although preferred embodiments have been disclosed and described indetail herein, its scope and objects should not be limited thereby;rather its scope should be determined by that of the appended claims.

1. An improved seam in an industrial fabric comprising: a plurality ofwelded portions in a seam area of the fabric, wherein welding in saidwelded areas is formed by applying a laser energy absorbing material ina controlled manner, and focusing a laser source at said material,thereby partially melting and permanently welding the fabric at saidportions, and wherein said welding is formed on a yarn surface.
 2. Theseam of claim 1, wherein said seam has properties such as openness,contact points, and Fiber Support Index (FSI) which is the same orsubstantially the same as the fabric body.
 3. The seam of claim 1,wherein said seam strength and durability is greater than normal if theseam has the same design and length as normally used for this particulardesign.
 4. The seam of claim 1, wherein a width of said seam as measuredin MD is a fraction of a width of a normal seam or a seam formed usingconventional techniques, said fraction being 0.7 or lower.
 5. The seamof claim 1, wherein the welded seam area eliminates terminal endpullback.
 6. The seam of claim 1, wherein the laser energy absorbingmaterial is applied by dye coating on said yarns before being woven intothe fabric or deposited onto said fabric after being woven, in acontrolled manner in a predetermined pattern.
 7. The seam of claim 1,wherein said welding is in the form of bands in a cross machinedirection of the fabric.
 8. The seam of claim 1, wherein said laserenergy absorbing material is an aqueous based dye.
 9. The seam of claim1, wherein said laser energy absorbing material is a solvent based oraqueous based dye to achieve a textured or smooth yarn surface duringwelding respectively.
 10. The seam of claim 1, wherein the yarn shape,size, properties are the same or substantially the same as an unweldedyarn.
 11. The seam of claim 1, wherein portions are multiple crossoverpoints along the length of a single warp or weft yarn.
 12. The seam ofclaim 1, wherein said welding is carried out as a combination of spotwelds, and bands in cross machine direction of the fabric.
 13. The seamof claim 1, wherein said fabric comprises grooved yarns.
 14. The seam ofclaim 1, wherein said seam is a pin seam or an inline spiral seam. 15.The seam of claim 1, wherein a width of said seam as measured in MD is afraction of a width of a normal seam or a seam formed using conventionaltechniques, said fraction being 0.5 or lower.
 16. The seam of claim 1,wherein a width of said seam as measured in MD is a fraction of a widthof a normal seam or a seam formed using conventional techniques, saidfraction being 0.3 or lower.